Caption: Photosynthesis electron transport complex. Illustration of cyclic electron transport taking place as part of Photosystem I in photosynthesis on the thylakoid membrane (blue) of a plant's chloroplast. The electrons (e-) are being cycled around a cytochrome b/f complex (pink), a complex of proteins that are embedded in the membrane. The electron transport is partly carried out by the iron-sulphur protein ferredoxin. Protons (H+) are also shown. At right is an ATP synthase protein complex (red), which produces ATP (adenosine triphosphate). For this artwork with labels, see image C023/8817.